SLS finally announced by NASA – Forward path taking shape

After several years of trade studies and political arguments, NASA administrator Charlie Bolden finally gave the Space Launch System (SLS) its official public unveiling on Wednesday. As has been known for months, the Heavy Lift Launch Vehicle (HLV) is Shuttle Derived (SD) and will use $10 billion of NASA funding through to its debut launch in 2017.

SLS History:

Not unlike most launch vehicles, SLS has suffered from a complicated birth, most of which was not of its own doing – as the political element of NASA decision making process questioned the motives of the design, and even the need for a HLV.

Regardless, the wait is now over, as the in-line SD HLV has finally been revealed in the official arena, after a heavily delayed announcement by General Bolden – flanked by lawmakers – on Wednesday.

“The next chapter of America’s space exploration story is being written, right here, right now. We’ve selected the design for a new space exploration system that will take humans far beyond Earth. This important decision will create high-quality jobs here at home and provide the cornerstone for America’s future human space exploration efforts,” noted the General in an address to employees.

RAC-1 studied in-line, LH2 core vehicles with Solid Rocket Boosters (SRB). While this vehicle was based around the SD HLV, the teams avoided the use of such a name, given they were allowed to trade Space Shuttle Main Engines (SSMEs) with RS-68s, while also trading SRBs with Liquid Rocket Boosters (LRBs), in order to ensure they have the best configuration to battle with the other HLV candidates.

RAC-2 studied a Saturn V-type vehicle, utilizing an RP-1 first stage and LH2 second stage. Like RAC-1, the team was allowed to trade different engine options, within their designated configuration. RAC2 included SpaceX’s Falcon XX (huge vehicle with six Merlin 2 engines) in the trades. Ironically, the announced SLS was given the fanfare of being more powerful than the Saturn V.

RAC-3 studied vehicle designs based around several options, such as EELVs, with a large amount of latitude to study different tank sizes, including the evaluation of clusters of Atlas-sized tanks similar to how the Saturn IB first stage was built.

While some people associated with losing vehicle options claim the study process was automatically aligned to favor the SD HLV, this configuration officially won, as the records show.

The July 8 announcement, which was even noted by Atlantis’ commander Chris Ferguson, was then cancelled, as a stalling process was put into effect, apparently under the order of the White House. This process was classed as a requirement for an independent costing assessment, to be carried out by Booz Allen. Such a process would delay the final report yet further.

Even after the cost assessment process was complete, no announcement was made, much to the anger of several Senators involved with the Authorization Act, brought to a head when a – somewhat mis-written – cost overview was leaked to the Wall Street Journal, in what is claimed to be an attempt to create large-scale opposition from within the space community.

It backfired, as the leaked report caused several meetings between political and NASA heads, based around revealing the true cost estimate findings, and ultimately leading to a joint agreement between all relevant bodies. This agreement paved the way for Wednesday’s official announcement of the vehicle.

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“This launch vehicle decision is the culmination of a months-long, comprehensive review of potential designs to ensure that the nation gets the best possible rocket for the investment – one that is not only powerful but is also evolvable so it can be adapted to different missions as opportunities arise and new technologies are developed,” added General Bolden.

“The selection of the vehicle needed to transport our astronauts beyond low Earth orbit is one of the most important decisions NASA will make this decade, and it requires a major commitment on the part of the American people. That’s why we took the time to get it right.

“The hard work and expertise of you in the NASA Family have brought us to this point and will be critical as we continue to do the big things only NASA can do and challenge ourselves as a people to reach our highest potential. The future is bright for exploration, and we can be proud of the major step forward we are taking today.”

SLS – The Vehicle:

Heavily based on Shuttle heritage hardware, the design of the vehicle has been known for some time – as reported by this site. There will be two major roles for SLS, one is to launch cargo and one to launch the Orion (MPCV).

The core stage is an 8.4m diameter “External Tank” heritage system, with the top converted to host the Upper Stage structure, and the aft restructured to house the Main Propulsion System (MPS) – which will drive what will initially be three Space Shuttle Main Engines (RS-25Ds).

The system is designed to eventually fly with five engines in the core.

The role of Pratt & Whitney Rocketdyne (PWR) is now official, with SLS’ path towards its 2017 IOC (Initial Operating Capability) ready to utilize the 12 RS-25Ds available for one-off roles with SLS flights, following their transition from the Space Shuttle Program (SSP).

It has also been confirmed that there will be a transition to the expendable version of the SSME, known as the RS-25E, either after the four sets of RS-25Ds have been used, or after two additional RS-25D sets have been manufactured – per reserved stock at PWR.

The eventual engine driving the core stage is confirmed as the RS-25E, a cheaper engine due to its expendable nature.

Discovery’s MPS is likely to be used on test structures, while Atlantis and Endeavour’s MPS are likely to ride with SLS-1 and SLS-2.

Final evaluations are taking place into this $20m effort, with the next SLS article to overview the latest status presentations (L2).

SLS-1 and potentially SLS-2 will ride with ATK’s five segment boosters, although the competition for the confirmed booster of choice for the remainder of SLS’ lifetime will begin shortly.

With the Core designed to be compliant with several booster options – so as not to prejudice to the competition – working with commonality on the core interfaces, and standard approach of the boosters providing stability for the vehicle when attached to the pad, will be some of the baseline requirements.

While the competition will involve a number of booster options, ATK have already published a statement showing their confidence in continuing with SLS through its lifetime.

“ATK applauds NASA’s decision to move forward with a Space Launch System for human deep space exploration. We are proud that NASA will utilize ATK’s five-segment solid rocket motors as the baseline design for the initial flights,” noted the Utah-based company.

“ATK’s five-segment boosters provide unmatched capability and we will deliver this performance within the current budget. We are confident in the design and look forward to the early test flights to demonstrate our capability.

“We are also well positioned to compete for the final design because of our proven performance and a thrust-to-weight ratio of our solid rocket motors which are ideally suited for first stage propulsion.”

Such potential upgrades to the booster may include recently proposed change to a HTPB (Hydroxyl-terminated polybutadiene) fueled solid in “composite over wrapped steel cases” thus allowing higher MEOP (Maximum Expected Operating Pressure) – to as much as 1500 psi. This could become key, with NASA mentioning the competition will be mainly looking into the performance numbers of the booster candidates.

As previously reported, there are also proposals to use lighter weight nozzles with expansion ratios up to 12:1, although such a large scale change would require study at least at a Ground Support Equipment (GSE) level, given its relation to Launch Platform design.

A second ML, or a major conversion to the Shuttle Mobile Launch Platform (MLP-3), will be the likely options available to the Ares-1 style vehicle.

The SLS vehicle is being designed with an Upper Stage, which will be evaluated up to the Preliminary Design Review (PDR) stage. This Upper Stage will be driven by the Constellation-born J-2X engine, currently undergoing initial testing at the Stennis Space Center.

The vehicle will be able to fly without the Upper Stage, and in some cases would fly with a smaller replacement in the form of a Delta IV “Kick Start” Upper Stage system.

SLS will not be decked out in the Saturn V “White and Black” paint, as seen in graphics of the vehicle, which sources note was only for publicity purposes. The vehicle will sport the orange “spray applicated” Thermal Protection System (TPS) foam, as seen on the Shuttle External Tanks.

SLS – Forward Work:

It now appears – as noted at the time – that the initial schedules and costings (leaked or otherwise) were based on worst case estimations, with only the 2017 opening launch date for the vehicle confirmed during Wednesday’s announcement.

Instead, an increased flight rate, based mainly on finding additional uses of the large fairing design and upmass capability of SLS, has been intimated. Former Space Shuttle Program (SSP) manager John Shannon has also been tasked with creating a schedule and mission architecture for the vehicle.

Work on a schedule and funding path is being worked internally by NASA and in the political arena, but as of this week, no long-term schedule can be cited until the key driver of the funding profile – which is classed as still under consideration, and not final – is officially created.

A lot will depend on what the Congress is able to provide through the annual appropriations process, with the only “official” targeted flight being SLS-1, in 2017. This date is set, with no allowance for it to slip to the right, even in the event of unexpected funding issues.

Work on later goals – such as the Upper Stage for the 130mt version of SLS, or mission content for SLS flights – would instead be slipped or re-worked to protect the 2017 date, which is likely where the “worst case” 2021 date for SLS-2 – and the low flight rate through to 2032 – was formed, based on a scenario where initially achieving the 2017 IOC date suffered from major issues.

Wednesday’s official announcement is vital to SLS, as it enables NASA to now have an approved, focused program planning effort to initiate work that will lead to the usual Systems Requirements Review and Preliminary Design Reviews.

This will lead to final determination of cost and schedule, as is normally the case with any new major vehicle development.

Next up on this path will be the procurement process, which includes meetings this week, through to next week, ahead of an industry day meeting later this month.

As mentioned, the core stage work will be the main opening challenge for the engineering teams, which in turn will drive the vehicle’s major milestone of the PDR, currently scheduled for early 2013.